Silver bleach for color materials



Patented May 9, 1950 SILVER BLEACH FOR COLOR MATERIALS Lot S. Wilder,Rochester, N. Y., and Kent 0.

Brannock, Oak Ridge, Tenn., assignors to Eastman Kodak Company,Rochester, N. Y., a corporation of New Jersey No Drawing. ApplicationMarch 23, 1945, Serial No. 584,494

1 Claim.

This application relates to color photography and particularly to theremoval of silver images from emulsion layers in color photography.

In photographic color processes in which a colored image is formed bydevelopment with a primaryaromatic amino developing agent in thepresence of a coupler compound, the silver images formed duringdevelopment are present in the. emulsion layer together with dye images.These silver images are generally removed by converting them to a silversalt which is soluble or which is removed by hypo. A bath of this typecontaining potassium ferricyanide and potassium bromide is disclosed inMannes, Godowsky and Wilder U. S. Patent 2,252,718, granted August 19,1941.

Silver bleach baths containing quinone and an acid have also been usedfor removal of silver. A bath of this type is disclosed in Mannes andGodowsky U. S. Patent 2,113,329, granted April 5, 1938. These quinonebleach baths cannot be used in the final stages because they destroy theimage dyes as well as convert the silver to a silver salt. A quinonebleach bath suitable for removal of silver in the presence of a dyeimage is described in Vittum U. S. patent application Serial No.541,843, filed June 23, 1944, now abandoned.

Quinone bleach baths are inconvenient to prepare because the quinonedissolves very slowly in aqueous solutions. The common organic solventsare inconvenient or adversely influence the solution. Quinone is quicklysoluble in hot glacial acetic acid, but this requires handling hotliquid and is an inconvenience in the preparation of the bleach bath.Any liquid is undesirable where the ingredients of the bath must bepackaged for sale and kept for a period of time before being purchasedby the ultimate user.

It is, therefore, the principal object of the present invention toprovide a simple and convenient method for the preparation of quinonebleach baths for use in color photography. A further object is toprovide a bleach bath which may be packaged and kept in dry form. Otherobjects will appear from the following description of our invention.

These objects are accomplished by using as the source of the quinone amixture of hydroquinone and an oxidizing agent for the hydroquinonewhich converts it to quinone in acid solution. Suitable oxidizing agentsfor this purpose are alkali metal salts of oxygen acids capable ofoxidizing hydroquinone to quinone. Suitable alkali metal salts are thesodium, potassium, and ammonium salts, such as ammonium persulfate,potassium permanganate and potassium dichromate.

In the preparation of bleach baths according to our invention, thehydroquinone is mixed with solution may contain glacial acetic acid asin the case of the prior art quinone bleach baths, although this isunnecessary. Acids which may be used include hydrochloric and sulfuricacid, or the acid may be obtained in solution from sodium acid sulfateor sulfamic acid. The bleach bath also may contain a soluble bromide orchloride to cause the formation of silver halide from the oxidizedsilver.

When packaged in dry form, the bleach baths of our invention preferablycontain the hydroquinone in one compartment and the oxidizing agent andpotassium bromide in another compartment. If a dry acid former, such assodium acid sulfate, is used, it may be placed in the container with thehydroquinone. By acid former we mean a substance which forms an acidwhen dissolved in water, such as sodium acid sulfate, sulfamic acid,etc.

The following formulas illustrate bleach baths prepared according to ourinvention.

Formula 1 Hydroquinone g 2.5 Ammonium persulfate g 5.14 Potassiumbromide g 10 Glacial acetic acid cc 5 Hydrochloric acid (conc.) cc 5Water to 1 liter.

Formula 2 Hydroquinone g 2.5 Potassium permanganate g 1.4 Potassiumbromide g 10 Sulfuric acid (conc.) cc 1 Glacial acetic acid cc 5Hydrochloric acid (conc.) cc 5 Water to 1 liter.

Formula 3 Hydroquinone g 2.5 Potassium dichromate g 2.2 Potassiumbromide g 10 Sulfuric acid (conc.) cc 1 Hydrochloric acid (conc.) cc 5Water to 1 liter.

The following formula illustrates a dry powder mixture for preparing oneliter of solution according to our invention:

Formula 4 A NaHSO g 28 Hydroquinone g 1.25

B Potassium dichromate g 1.5 Potassium bromide g 10 3 Formula 5 Sulfamicacid g 12 Hydroquinone g 1.25 Potassium dichromate g 1.5 Potassiumbromide g 10 Water to 1 liter.

In place of quinone, derivatives of quinone, such as chloroquinone ortoluquinone. may be used. The bleach bath in use isfollowed by a dilutesolution of sodium bisulfite, for example, a 1% solution of bisulfite toreact with the retained quinone, and the photographic element is thenfixed for about 4 minutes in hypo, washed and dried.

It will be understood that the examples and formulas included herein areillustrative only and that our invention is to be taken as limited onlyby the scope of the appended claim.

We claim:

A dry powder composition for preparation of an acid quinone bleach bathby mixing with water, comprising hydroquinone, sodium hydrogen sulfate,and potassium dichromate.

LOT S. WILDER. KENT C. BRANNOCK.

4 REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,755,129 Pomeroy Apr. 15, 19301,755,130 Pomeroy Apr. 15, 1930 1,966,330 Burwell July 10, 19341,969,479 Seymour Aug. 7, 1934 2,019,718 Mannes et a1 Nov. 5, 19352,059,881 Mannes et a1 Nov. 3, 1936 2,113,329 Mannes et a1 Apr. 5, 19382,158,186 Hickman et a1 May 16, 1939 2,195,419 McQueen Apr. 2, 19402,313,523 Donovan et a1 Mar. 9, 1943 OTHER REFERENCES Conant, TheChemistry of Organic. Com.-

20 pounds, The Macmillan 00., New York, 1936;

